1. Field of the Invention
The invention relates to a running pattern calculating apparatus and a running pattern calculating method.
2. Description of the Related Art
The increase in the price of crude oil last year and the need for technology to improve the environment by reducing CO2 and the like have made improving fuel efficiency a top priority. In the past, coasting has been empirically known as an ideal way to improve fuel efficiency in eco-run competitions to see how many kilometers a vehicle can travel on a circuit or the like on only one liter of gasoline, for example. Also, in a vehicle in which the engine can be stopped while the vehicle is traveling, such as with a hybrid system (HV), stopping the engine while the vehicle is traveling is known as an effective way to improve fuel efficiency when the vehicle is traveling.
The ultimate improvement in the fuel efficiency of vehicles is to run vehicles according to optimal running patterns rather than according to the intentions of the users (i.e., the drivers). Test results and the like have shown that doing so yields improvements in fuel efficiency of more than 30%. In recent years, optimization methods for optimizing the running pattern and the speed ratio have been developed using an evaluation function such as fuel efficiency in order to provide running assist and automatic running control in vehicles (see Japanese Patent Application Publication No. 2002-251597 (JP-A-2002-251597) and Japanese Patent Application Publication No. 10-246325 (JP-A-10-246325). These optimization methods here generally presume that running patterns that have been newly generated from previous generated running patterns are closer and closer to the ideal solution. That is, the optimization technology is technology that assumes that there must be a pattern C that is ultimately better than an operating pattern B that is in turn relatively better than a given operating pattern A, and therefore arrives at the pattern C, which is the optimum solution, by repeating the process of transforming the given operating pattern A to the operating pattern B, based on that assumption. The optimization method assumes that the best pattern is an extension of a pattern that is better than the current pattern, and there are no worse patterns in between.
However, when attempting to apply the optimization method to fuel efficiency evaluation, the engine has a discontinuous characteristic in which the efficiency is worst at low engine speeds (such as approximately 800 rpm (idle speed) to 1500 rpm) and good at an engine speed of zero as well as at medium and high engine speeds. Therefore, even if the evaluation function process is repeated in an attempt at total optimization, a running pattern having a running state that stops the engine (i.e., zero rpm) is unable to be obtained, and as a result, an operating pattern obtained by the optimization method performed to improve fuel efficiency does not necessarily end up to be a fuel efficient operating pattern. That is, when the related optimization method is applied as it is, the engine efficiency conversely decreases in a region (near a low engine speed) where the engine speed decreases toward zero (at which the engine is stopped) from an engine speed where the engine efficiency is good (i.e., a medium or high engine speed), so the fuel efficiency becomes worse and an operating pattern that includes low vehicle speeds ends up being rejected. As a result, the engine efficiency falls to the local minimum and a running pattern that is ideal for fuel efficiency, the vehicle alternately accelerates and coasts repeatedly etc., is not able to be reached.
Therefore, the local minimum problem caused by discontinuity in the thermal efficiency between when the engine is operating and when the engine is stopped is avoided, and the running pattern related to fuel efficiency or the like is optimized, by fixing an operating pattern that includes accelerating and coasting, and giving up on total optimization as a restraint condition. Here, the method described in Japanese Patent Application Publication No. 2006-327545 (JP-A-2006-327545) is a method for improving the movement results with respect to fuel efficiency or the like by setting a restraint condition to restrain movement when a moving object is traveling in a section from a point of departure to a point of arrival. For example, a fuel efficient operating pattern is generated by establishing a restraining condition by setting a fixed operating pattern in a range in which a process of acceleration steady travel deceleration, for example, occurs once.
Also, Japanese Patent Application Publication No. 2007-187090 (JP-A-2007-187090) and Japanese Patent Application Publication No. 2007-291919 (JP-A-2007-291919) describe methods that improve fuel efficiency characteristics by storing maps related to speed and vehicle-to-vehicle distance in advance and determining whether the vehicle is coasting or the like by checking against the stored map, instead of by evaluating the fuel efficiency or the like according to an evaluation function.
However, in the related optimization method, although localized optimization is performed with respect to fuel efficiency or the like, total optimization will not necessarily be achieved.
In particular, with the method described in JP-A-2006-327545, when a general travel plan in which accelerating and coasting are repeated is estimated, it provides fuel efficient running in parts so there are localized improvements in fuel efficiency. However, a repetitive pattern that is based on a calculation that will further improve the overall fuel efficiency from departure to arrival while the vehicle is actually traveling is not generated. That is, in the actual running environment, it is necessary to obtain a continuous solution, such as that shown in FIG. 17 of JP-A-2006-327545. However, the method described in JP-A-2006-327545 simply appropriates the results of a fixed pattern and does not include adjustments of the specific acceleration and the like in parts. Therefore, separate changes must be made to obtain total optimization.
Also, with the methods described in JP-A-2007-187090 and JP-A-2007-291919, although localized improvements in fuel efficiency are realized using the maps related to speed and vehicle-to-vehicle distance, these publications do not consider total optimization.
Also, with respect to required acceleration following an actual driving operation by the driver, JP-A-2006-327545 does not consider how to coordinate driver operations with vehicle control based on a target operating pattern in order to bring the actual operating pattern closer to the target operating pattern. Accordingly, there is room for improvement to more efficiently coordinate driver operations with vehicle control based on a travel plan.